Blood pressure has long been known as an important factor in the evaluation of the general level of health of an individual. Blood pressure is typically measured by a so-called auscultatory method using a sphygmomanometer where an inflatable cuff is placed over an extremity of a subject and inflated to a pressure at which circulation is halted in the extremity and then deflated while the subject's pulse and circulation are aurally monitored with a stethoscope or the like. Since the inflatable cuff imposes pressure on the extremity against the natural elasticity of the flesh of the extremity, the circulation in different depths below the surface of the flesh in the extremity will be affected at different pressures. Upon deflation after circulation is halted in the extremity, circulation will resume in deep tissues at a first pressure, referred to as the systolic pressure, reflecting the maximum pressure developed by the heart and at a second, lower pressure, known as the diastolic pressure, in the shallow tissues near the surface of the extremity which reflects the minimum pressure against which the heart must work.
When the above procedure is performed, it is necessary for it to be performed by a person other than the person whose blood pressure is being measured since muscular tension necessary to control deflation of the cuff or to position a listening device such as a stethoscope will affect the accuracy of the measurement. Also, the ability to hear the differences in circulation will be reduced, since circulation in the ear of the user will mask the subtle changes in the sounds caused by changes in circulation in the extremity during control thereof by the inflatable cuff.
In recent years, the increase in "health-consciousness" on the part of some individuals has led to the development of personal automated devices for measuring blood pressure and pulse rate. While the cost of such devices is not great and their availability is reasonably widespread, such devices are likely to be regarded as unnecessary or a luxury for private ownership unless strongly recommended by a physician having already diagnosed hypertension in the individual. Thus, such devices are not likely to result in the discovery of hypertension or other conditions for which treatment should be sought.
On the other hand, it has become increasingly apparent in recent years that hypertension, or elevated blood pressure, is a major, generally undiagnosed, condition since it is not accompanied by symptoms which would typically lead an individual to seek medical attention. Over a period of time, undiagnosed or untreated hypertension may cause substantial damage or degeneration to the heart and circulatory system. Such undiagnosed and/or untreated hypertension has been found to be a major factor in the development of heart disease or the occurrence of heart attacks. Further, abnormal blood pressure may be a major indicator of the existence of an aneurism, an enlargement of a blood vessel which has an increased likelihood of bursting with often catastrophic consequences and high mortality rate.
To provide such availability of blood pressure testing, it has become common for medical institutions such as hospitals to provide screenings for high blood pressure and other conditions. Such screenings have the advantage of providing trained personnel to test and counsel large numbers of people. However, such screenings are expensive to the institution providing them and involve administrative and other expenses such as advertising and publicity. While such screenings have been fairly successful at raising public awareness of particular health problems, they often do not succeed in promoting follow-up testing or treatment, particularly where the physical parameter tested is subject to wide variation due to many causes, as is the case with blood pressure. Further, there may be a perceived lack of confidentiality in such screenings and the potential adverse effects of seeking information concerning hypertension on insurance premiums may deter an individual from seeking information concerning his or her condition.
Accordingly, it has recently become apparent that there is a need for the ready availability to the public of apparatus to measure blood pressure. Such availability provides the equivalent of screening by trained personnel, which, while generally accurate and offering the possibility of providing advice and counseling when results are abnormal, suffers from the drawbacks of expense, irregular and inconvenient availability, a perceived lack of privacy and confidentiality and the likelihood that a significant result will be dismissed by the subject due to the unusual circumstances of the screening itself. It is also well-known that hypertension cannot be reliably diagnosed on the basis of a single blood pressure measurement but requires several consistently high measurements to reliably indicate the condition.
Even after diagnosis of hypertension, it is necessary to periodically monitor blood pressure. The expense or inconvenience of obtaining such measurements may impede or interfere with treatment. Even the personal blood pressure monitors alluded to above may constitute a relatively large expense and an alternative to ownership of such a device is necessary.
Recently, therefore, it has been found to be effective in the early detection of hypertension to provide automated blood pressure testing apparatus in public places either as a public service or on a pay-per-use basis. This has been found to be particularly effective in pharmacies and other commercial establishments which also distribute prescription medications because of the availability of a pharmacist who can give independent confirmation of the need to consult a physician if blood pressure measurements are consistently high. Installation of such automated blood pressure measuring devices has also been found to be beneficial to the commercial establishments providing them and such installations have proven to be a substantial source of income when installed on a pay-per-use basis as well as enhancing sales of other products. Such installations allow blood pressure tests to be done conveniently and at intervals over a substantial period of time and with a fairly high degree of confidentiality.
One example of a suitable device is disclosed in U.S. Pat. No. 4,729,382, filed on Sept. 2, 1986, and issued to joint inventors herein Jon D. Schaffer and George L. McDade entitled METHOD AND APPARATUS FOR AUTOMATICALLY DETERMINING PULSE RATE AND DIASTOLIC AND SYSTOLIC BLOOD PRESSURE which disclosure is fully incorporated by reference herein. Details of the operation of the basic device which are not necessary to a full understanding of the present invention are omitted herein in the interest of clarity and full disclosure of such details may be found in the patent incorporated by reference.
With regard to the basic device, it has been found that, for installation in a commercial establishment, a stand is desireable due to the high cost of floor space. Further, and for the same reason, it has been found desireable to provide such a stand which allows the basic device to be used when the user is in a standing position. Use in a standing position is also desireable since the device can be used less conspicuously in a store environment where it is unusual for a customer to sit. However, such an installation presents a problem since the standing posture of a user is not typical of standard postures in which blood pressure is commonly measured. Specifically, when done by medical personnel, blood pressure is typically measured at the upper arm with the subject either seated or recumbent so that the inflatable cuff used in the measurement will be located at heart level. It is highly desireable, in this regard, considering potential use by users who may be screening themselves for hypertension and those who use the device as an aid to medical treatment that the measurements made by the device be accurately and consistently correlated with measurements made by trained medical personnel using sphygmomanometers. It has also been found to be desireable that the inflatable cuff be rigidly mounted to the housing of the device as shown in U.S. Patr. Des. No. 298,167, filed Dec. 6, 1985, and also issued to joint inventors herein Jon D. Schaffer and George L. McDade. This arrangement provides for protection of pneumatic parts which are vulnerable to tampering and vandalism and permits the pressure cuff, pump and valves to be assembled in a module which can be readily replaced for ease of servicing in the field. The device is also intended to take blood pressure measurements from the forearm of the user which has been found to be highly accurate in accepted invasive methods of blood pressure measurement using an arterial catheter. Use of the forearm of the user for blood pressure measurements is also a matter of convenience to the user, particularly in the intended application, since a comfortable and natural posture can be maintained which does not draw attention to the user. For much the same reasons, and also the additional fabrication and possible maintenance expense involved, it is not deemed to be reasonably practical to provide for alteration of the height of the entire machine in an attempt to standardize posture since that effect would not be achieved in any event without substantial other structure impeding ease and discreteness of use. Further, use of the forearm does not require the upper arm to be exposed and therefore does not require sleeves to be fully rolled up, thus avoiding the binding effect of clothing which may affect measurement results. However, unlike techniques using the upper arm, the cuff is not assured to be at or near heart level and, therefore, errors due to differences in hydrostatic pressure due to the difference in height between the heart and the inflatable cuff may cause substantial differences between the actual measurement made and the value which would have been obtained if the subject were in a more standard position or posture for measurement of blood pressure.